1. Field of the Invention
This invention relates to an excipient for a pharmaceutical tablet and, more particularly, to an excipient which is a proliferous copolymer of vinyl pyrrolidone and vinyl acetate, providing the tablet with both rapid dissolution and disintegration properties, and reduced hygroscopicity.
2. Description of the Prior Art
Zhong, Y. et al, in U.S. Pat. No. 5,663,258, described a strongly swellable, moderately crosslinked copolymer of vinyl pyrrolidone and vinyl acetate made by precipitation polymerization in the presence of a free radical initiator. The copolymer obtained by this process had unique gel volume and viscosity properties which enabled it to thicken aqueous and non-aqueous solutions effectively. Meffert, H., in EP 0979649A2, also described copolymers of vinyl pyrrolidone and vinyl acetate made by free radical polymerization, optionally with an added crosslinking agent, which process provided copolymers having K-value of 50 to 200. Such copolymers were considered suitable for use as a matrix material in pharmaceutical or cosmetic preparations.
Blankenburg, R. et al, in U.S. Pat. No. 5,635.169, also described a free radical process for making copolymers of vinyl pyrrolidone and vinyl acetate having a K-value of 30-50 for use in cosmetic formulations.
Tseng, S. et al, in U.S. Pat No. 5,393,854, described the preparation of the isomeric compound 1-vinyl-3(E)-ethylidene pyrrolidone (EVP) having the formula: 
which, in solid form, had a purity of at least 95% and were white, needle-shaped crystals having a melting point of 59-61xc2x0 C. This isomeric compound was used as a crosslinking agent in the proliferous polymerization of vinyl pyrrolidone.
Tseng, S. et al in U.S. Pat. No. 5,393,854, also described a polyrmerizable composition of vinyl pyrrolidone and isomeric EVP for proliferous polymerization of vinyl pyrrolidone.
Accordingly, it is an object of the present invention to provide a proliferous copolymer of vinyl pyrrolidone and vinyl acetate for use as efficient excipient for drugs, which provides the drug tablet with both rapid dissolution and disintegration properties at predetermined pH levels, and reduced hygroscopicity.
What is described herein are pharmaceutical excipients for drug tableting which are proliferous copolymers of vinyl pyrrolidone (VP) and vinyl acetate (VA), which provides the tablets with both rapid dissolution and disintegration properties, and reduced hygroscopicity. In particular, the proliferous copolymers of vinyl pyrrolidone and vinyl acetate of the invention exhibit comparably rapid dissolution and disintegration properties under aqueous acidic conditions as compared to a proliferous polyvinylpyrrolidone homopolymer, as well as excellent moisture resistance (reduced hygroscopicity) in the dry state (which is attributed to their increased hydrophobicity).
The pharmaceutical tablet releases at least 80% of the drug within 20 minutes and 100% within 35 minutes, under aqueous acidic conditions, and picks up less than 14.6% moisture at a constant humidity value of 55%.
A typical proliferous copolymer of the invention consists essentially of, by weight, about 60-90% VP, about 10-40% VA, and crosslinker, preferably about 75-82% VP, about 18-25% VA and about 0.8-1.2% crosslinker.
The proliferous copolymer of the invention is made by providing a polymerization mixture of, VP, VA and crosslinker, at a temperature of about 80-100xc2x0 C. heating until proliferous polymerization occurs, and then recovering the desired copolymer.